Method for producing acetic acid

Abstract

A method for producing acetic acid according to the present invention is a method for producing acetic acid comprising: a carbonylation reaction step; an evaporation step; a lower boiling point component removal step; and a first overhead stream recycle step of recycling at least a portion of an aqueous phase and/or an organic phase obtained by condensing a first overhead stream obtained in the lower boiling point component removal step to a reaction vessel, wherein a crotonaldehyde concentration in a first acetic acid stream obtained in the lower boiling point component removal step is controlled to not more than 2.2 ppm by mass. The catalyst system may further contain an ionic iodide. The method for producing acetic acid may further comprise an acetaldehyde separation and removal step of distilling at least a portion of the aqueous phase and/or the organic phase obtained by condensing the first overhead stream to separate and remove acetaldehyde.

The invention claimed is: 
     
       1. A method for producing acetic acid, comprising:
 a carbonylation reaction step of reacting methanol with carbon monoxide in the presence of a catalyst system containing a metal catalyst and methyl iodide, as well as acetic acid, methyl acetate, and water in a reaction vessel to produce acetic acid; 
 an evaporation step of separating a reaction mixture obtained in the carbonylation reaction step into a vapor stream and a residual liquid stream in an evaporator; 
 a lower boiling point component removal step of separating the vapor stream by a first distillation column into a first overhead stream rich in at least one lower boiling point component selected from methyl iodide and acetaldehyde, and a first acetic acid stream rich in acetic acid, and condensing and separating the first overhead stream to obtain an aqueous phase and an organic phase; and 
 a first overhead stream recycle step of recycling at least a portion of the aqueous phase and/or the organic phase obtained by condensing the first overhead stream to the reaction vessel, 
 wherein a crotonaldehyde concentration in the first acetic acid stream is controlled to not more than 2.2 ppm by mass; and 
 a ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is not more than 35; 
 further wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by at least one of (a) controlling a hydrogen partial pressure in the reaction vessel to not less than 0.02 MPa and no more than 0.5 MPa or (b) controlling a reflux ratio during the lower boiling point component removal step to not less than 2 and no more than 100. 
 
     
     
       2. The method for producing acetic acid according to  claim 1 , further comprising:
 a dehydration step of separating the first acetic acid stream by a second distillation column into a second overhead stream rich in water and a second acetic acid stream more enriched with acetic acid than the first acetic acid stream; and 
 an overhead stream recycle step of recycling at least a portion of the aqueous phase and/or the organic phase obtained by condensing the first overhead stream, and/or a portion of the second overhead stream to the reaction vessel, 
 wherein the crotonaldehyde concentration in the first acetic acid stream is controlled to not more than 2.2 ppm by mass, and a reflux ratio of the second distillation column is controlled to not less than 0.32 and no more than 100. 
 
     
     
       3. The method for producing acetic acid according to  claim 2 , wherein a crotonaldehyde concentration in the second acetic acid stream is not more than 2.0 ppm by mass. 
     
     
       4. The method for producing acetic acid according to  claim 2 , wherein a 2-ethyl crotonaldehyde concentration in the second acetic acid stream is not more than 3.0 ppm by mass. 
     
     
       5. The method for producing acetic acid according to  claim 2 , wherein a ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the second acetic acid stream is not more than 35. 
     
     
       6. The method for producing acetic acid according to  claim 2 , wherein a butyl acetate concentration in the second acetic acid stream is not more than 15 ppm by mass. 
     
     
       7. The method for producing acetic acid according to  claim 2 , wherein a ratio of C CR /C BA  of the crotonaldehyde concentration C CR  in ppm by mass to the butyl acetate concentration C BA  in ppm by mass in the second acetic acid stream is not more than 2.0. 
     
     
       8. The method for producing acetic acid according to  claim 1 , wherein the catalyst system further contains an ionic iodide. 
     
     
       9. The method for producing acetic acid according to  claim 1 , further comprising an acetaldehyde separation and removal step of distilling at least a portion of the aqueous phase and/or the organic phase obtained by condensing the first overhead stream, to separate and remove acetaldehyde. 
     
     
       10. The method for producing acetic acid according to  claim 9 , wherein at least a portion of a residual liquid after separating and removing the acetaldehyde from at least a portion of the aqueous phase and/or the organic phase is recycled to the reaction vessel. 
     
     
       11. The method for producing acetic acid according to  claim 1 , wherein, for an operating condition of the first distillation column, when only the aqueous phase is refluxed to the first distillation column, a reflux ratio of the aqueous phase is not less than 2 and no more than 100; when only the organic phase is refluxed, a reflux ratio of the organic phase is not less than 1 and no more than 100; and when both the aqueous phase and the organic phase are refluxed, a total reflux ratio of the aqueous phase and the organic phase is not less than 1.5 and no more than 100. 
     
     
       12. The method for producing acetic acid according to  claim 1 , wherein a hydrogen partial pressure of the reaction vessel is not less than 0.01 MPa. 
     
     
       13. The method for producing acetic acid according to  claim 1 , wherein an acetaldehyde concentration in a reaction mixture liquid of the reaction vessel is not more than 500 ppm by mass. 
     
     
       14. The method for producing acetic acid according to  claim 1 , wherein a 2-ethyl crotonaldehyde concentration in the first acetic acid stream is not more than 3.0 ppm by mass. 
     
     
       15. The method for producing acetic acid according to  claim 1 , wherein a butyl acetate concentration in the first acetic acid stream is not more than 15 ppm by mass. 
     
     
       16. The method for producing acetic acid according to  claim 1 , wherein a ratio of C CR /C BA  of the crotonaldehyde concentration C CR  in ppm by mass to the butyl acetate concentration C BA  in ppm by mass in the first acetic acid stream is not more than 2.0. 
     
     
       17. The method for producing acetic acid according to  claim 1 , wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by (a) controlling a hydrogen partial pressure in the reaction vessel to not less than 0.01 MPa and no more than 0.5 MPa. 
     
     
       18. The method for producing acetic acid according to  claim 1 , wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by (b) controlling a reflux ratio during the lower boiling point component removal step to not less than 2 and no more than 100. 
     
     
       19. The method for producing acetic acid according to  claim 2 , wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by (a) controlling a hydrogen partial pressure in the reaction vessel to not less than 0.01 MPa and no more than 0.5 MPa. 
     
     
       20. The method for producing acetic acid according to  claim 2 , wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by (b) controlling a reflux ratio during the lower boiling point component removal step to not less than 2 and no more than 100. 
     
     
       21. The method for producing acetic acid according to  claim 2 , wherein the ratio of C CR /C ECR  of the crotonaldehyde concentration C CR  in ppm by mass to the 2-ethyl crotonaldehyde concentration C ECR  in ppm by mass in the first acetic acid stream is controlled to be not more than 35 by (c) controlling a reflux ratio of the second distillation column to not less than 0.32 and no more than 100.